Spectrographic instruments are used to provide accurate analysis of materials. The most common of these instruments is the spectrophometer. Spectrophometers measure intensity of light absorption and/or reflectance that occurs when a sample is exposed to electromagnetic radiation. Typically, spectrophotometers measure the absorption and/or reflectance of visible, near-ultraviolet, and near-infrared light. The main components of a spectrophometer include an electromagnetic radiation source, a chamber for holding a sample, and an electromagnetic radiation detector.
The function of a standard spectrophotometer can be briefly described as follows: (1) electromagnetic radiation at a specific wavelength is directed toward the sample; (2) the sample absorbs a specific amount or radiation; (3) the detector detects how much radiation the sample absorbed at the specific wavelength; (4) the detector converts the amount of radiation absorbed into a number; (5) the number is plotted on a graph and the process then repeats for a different wavelength until the full selected spectrum of electromagnetic radiation has been analyzed.
Spectrographic instruments can be used to determine measurable characteristics of the materials under analysis. For example, concentrations of constituents in the materials or alternatively, physical characteristics of the materials may be measured. In agriculture, spectrographic instruments are used to determine the oil, protein, and moisture content of grain, the fat content of meat, the fat, protein and lactose content of mile, and urea content of milk. Spectrographic instruments are also used to analyze blood samples, pharmaceuticals and synthetic resins.
It is well known when a number of spectrographic instruments measure the same sample, each instrument will generally produce an instrument specific signal if no actions are taken to ensure that the signals produced by the instruments are identical for a particular sample. The reasons for this include variation in the components for each instrument, variation in the instruments' age, repairs to a particular instrument, and fluctuations in the operating environment. It is equally well known that it is desirable to be able to manufacture spectrographic instruments which generate the same spectra absorption results when analyzing the same sample. There are some techniques in the field designed to correct for these problems.
Another dimension to the problems described above stems from the use of different spectrographic instruments from different manufactures. Large companies that make extensive use of spectrographic instruments often use instruments made by a variety of manufacturers. Price fluctuation is one reason for this. Another is that certain manufactures produce instruments for particular tasks. For example, manufacturer A produces an instrument specifically designed for moisture content of grain while manufacturer B produces instruments tailored for measuring the urea content of milk. A large agricultural firm would require the use of both instruments. But in order to calibrate both, the company would need to use the particular calibration system offered by each manufacturer to calibrate the respective machines. A plurality of calibration systems is expensive and makes it inconvenient to share information across instrument platforms.
Moreover, known techniques for multi-instrument calibration lack accuracy and ease of use. Some methods require measurements to be taken on the target instruments for a plurality of transfer samples. The transfer samples must contain known values for the property under consideration. Accordingly, if the operator of the target machine desired to analyze a new property in a sample, the operator would have to obtain transfer samples for the property in question that have been scanned in a reference instrument and then scanned in the target instrument before the operator can scan the target sample. This time-consuming procedure is not well suited for the modern production facility where efficiency is a top priority.
Other problems in the art include those associated with prediction methods for spectrographic instruments. The goal a prediction method when it is employed for a spectrographic instrument is to determine unknown properties of a sample. In other words, prediction methods allow for quantitative analysis. Whether the operator is looking for the fat content of a particular hybrid of wheat, or the octane level of gasoline, the operator can scan the sample, plug the scan results into the prediction method, and calculate a value for the property under analysis. A basic prediction method involves the use of a spectra library, mathematics, and equations that are applied to the product (spectra) library to generate a value for the unknown property of the sample.
The problem for an operator who is trying to improve his prediction method is the inability to easily expand the spectra library. Currently, spectra library expansion occurs only through persons who are highly skilled in the art of spectroscopy. In addition to the inability to easily expand the library, the continuous expansion of a spectra library may actually hurt the accuracy of predictions if the library becomes too large or redundant for the prediction method to properly sort through.
Therefore, there is a need in the art for a calibration system capable of calibrating spectrographic instruments regardless of manufacturer and regardless of the particular manufacturer's operation method and calibration method. In addition, there is also a need in the art for a system that can combine the multi-instrument calibration method discussed above with a method for accurately predicting properties about an unknown sample scanned in a spectrographic instrument.
A further need exists in the art for an easily-updatable spectra database and a prediction method that can access the database, as well as ensure that the accuracy of its predictions will not decline as the database expands. There is a need in the art for a system and method that combines both a calibration method and a prediction method that is easy to use for a spectrographic instrument operator. A need also exists in the art for a spectrographic system which has a high level of accuracy—both in its ability to produce consistent readings over the life of a particular spectrographic instrument as well as the ability of the spectrographic instrument to predict unknown properties of a sample.